Electrode spacer for electron discharge tubes



16, 1948. 3. SCHMIDT 2,437,972

ELECTRODE SPACERS FOR ELECTRON DISCHARGE TUBES Filed April '26, 1946 v m2: 2 muum...

. GERRII SCHMIDT INVENTOR ATTORNEY Patented Mar. 16, 1948 ELECTRODE SPACER FOR ELECTRON DISCHARGE TUBES Gerrit Schmidt, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, as trustee, Hartford, Conn.

Application April 26, 1946, Serial No. 665,023 In the Netherlands June 16, 1944 Section 1, Public Law 690, August s, 1946 Patent expires June 16, 1964 Claims.

This invention relates to an electric discharge tube comprising a spacer for electrodes and other parts in the tube, and more particularly to a discharge tube for very short waves.

Various constructions have already been used to ensure a reliable attachment of electrodes which is free from vibration. Thus, for instance, it is generally known to fix the electrodes with respect to one another by means of mica discs or plates, mica strips, glass beads or the like. These well-known constructions proved to be suitable for tubes in which the electrodes are comparatively widely spaced, for instance 0.5 mm. or more. One drawback is, however, that in the case of uneven heating of the various electrodes and the uneven expansion caused thereby, the

electrode spacing is slightly altered. Considering the comparatively wide spacing in tubes for great wavelengths this has only a slight influence, which is often negligible. However, these alterations become important in tubes for very short waves, in which the electrode spacing should be as small as possible, for instance smaller than 100p. and even a spacing of from 20 to 40a is desirable. It is obvious that a slight variation of these distances may involve a strong influence on the characteristics of the tubes. In addition, a spacer should involve as small as possible a capacity increase and, in view of the high frequencies the quantity of insulating material in the vicinity of the electrodes should be as small as possible; furthermore a small heat transfer between the electrodes is desirable. The common constructions are not satisfactory in these respects and this is an obstacle to securing a very small electrode spacing. A considerable improvement is obtained when making use of a spacer for electrodes and other parts of electric discharge tubes according to the invention. This spacer consists, for example, of a wire which is coated with insulating material and surrounded by metal parts each of which is secured to an electrode; these metal parts preferably have the form of rings that are slipped on the wire.

This construction yields a very rigid and firm attachment of the electrodes relatively to one another so that the electrode spacing may be very small. In a simple form of construction of a tube according .to the invention the said spacer consists of a wire of tungsten or molybdenum, which is coated with a thin layer of insulating material, e. g. magnesium oxide, aluminium oxide, beryllium oxide or the like, on which are slipped near each end one or more metal rings which may likewise consist of a material such as tungsten, molybdenum or the like. These rings are secured, for instance by welding, to the electrodes near the end. Uneven expansion of the electrodes in a direction normal to the connecting wire is taken up by a slight bending of this wire, which consequently must have a certain elasticity, so that it should not be too thick. A thickness of from to 200p. satisfies the requirements in regard to rigidity and elasticity; this thickness may slightly vary in accordance with the material used. In addition to the aforesaid metals tun sten and molybdenum, other materials having a low coefllcient of expansion and a low thermal conductivity e. g. nickel, nickel-iron, chromium nickel, or the like enter into account as a material for the core wire. A combination of these materials and the insulating coating results on the one hand in that the transfer of heat between the electrodes is as small as possible and on the other hand in that an execellent electrical insulation with low high frequency losses is maintained even at high temperatures.

As has already been set out above, it is advantageous for the metal parts secured to the electrodes to consist of rings that may be slipped, for instance in the form of closely wound helices, on the insulating layer; good results are obtained if the said rings have such a size as to embrace the insulating layer of the core wire. In a suitable form of construction a tungsten wire havin a thickness of to 200p is closely wound into the form of a helix. When securing these helices to an electrode by means of spot-welding in a nitrogen atmosphere practically no distortion occurs.

Members of the kind set out above are particularly suitable for use in discharge tubes for amplifying or producing electrical oscillations having very high frequencies, since they permit the use of a very small electrode spacing e. g. of from 20 to 40 The invention will now be more fully explained by reference to the accompanying drawing which represents, by way of example, a diode system for very high frequencies, in which:

Fig. 1 is a perspective view of an ultra-high frequency diode constructed in accordance with the invention; and

Fig. 2 is an end view of the diode of Fig. 1 without the envelope, heater, and lead-in wires.

Inthefigures,like numerals designate like parts. The reference number i designates the cathode and 2 the anode of the system. These electrodes are spaced by a member which, according to the invention, consists of a core or central wire 3 on to which is applied an insulating layer 4 and which is surrounded at both ends by helices 5 consisting. of several closely wound turns and being welded each to an electrode at 6. The electrode distance I, which may be 30 is not affected by expansion of the electrodes 1 and 2, since the helices 5 are placed near the edge of these electrodes. the core wire 3, located between the helices. 5 is practically negligible, notably if this core wire consists of a material having a low thermal conductivity and alow coeificient of expansion.

It has been found that these spacers permit the electrodes to be conveniently supported, particularly if a plurality of these members are used.

What I claim is:

1. An electric discharge tube comprising an envelope, two electrodes within said envelope, means maintaining a fixed distance between said electrodes comprising a spacer having a metallic core, an insulating coating around portions of said core, metal members attached to said coating and insulated from said corev by said coating, each of said metal members being attached to one of said electrodes, said spacer having a length between the points of attachment of saidmetal- 110 pieces to said electrodes of the order of magnitude of the distance of separation between said electrodes.

2. Anelectric discharge device comprising an envelope, two electrodes within said envelope each having an active face portion with an edge and means maintaining the spacing between said face portions comprising a central core wire, an insulating coating on said wire, two individual wires firmly wound about said coating, each said individual wires being attached near edge portions of said electrodes.

3. An electric discharge tube comprising an The expansion of the part of' envelope, two electrodes closely spaced relatively to each other within said envelope, means maintaining a substantially fixed distance between said electrodes comprising a, core wire, an insulating coating thereon, and a metallic member grasping said coating at each end of said wire and insulated from said wire by said coating, each said member being attached to one said electrode.

4. An electric discharge tube comprising an envelope, two electrodes within said envelope, means maintaining the spacing between said electrodes comprising a central core wire, an insulating coating on said wire, two wire helices each separately wound on said insulating coating and grasping said coating, each said helix being spot welded to one said electrode.

5. An electric discharge tube comprising an envelope, two electrodes within said envelope having active planar surfaces separated by a substantially predetermined distance, means maintaining the spacing between said electrodes comprising a central core wire, an insulating coating on said wire, two wire helices each separately tightly wound on said coating, each said helix being spot welded to one, said electrode with the length of said core wire between the closest of said spot welds being substantially equal to the said predetermined distance of separation.

GERRII SCHMIDT.

REFERENCES CITED UNITED STATES PATENTS Name Date Freeman Sept. 20, 1932 Number 

